This invention relates to automotive vehicle radar systems for detecting the presence of other vehicles in the vicinity and evaluating the possibility of a collision between the vehicles.
Currently there is great interest in developing systems that will allow an automotive vehicle to sense or detect other vehicles in its vicinity and determine whether a collision between the vehicles is likely. A vehicle-mounted radar system may be used to collect information about other vehicles or objects (generally known as targets) in the radar""s field-of-view and provide processed tracking information to other vehicle systems. When a collision between the vehicle and a target is likely or imminent, various actions can be taken to attempt to avoid the collision entirely or to mitigate the consequences of the collision. For example, automatic braking may be used to avoid the collision or to decrease the relative velocity of the collision. It is also possible to activate occupant protection devices on board the vehicle, such as airbags or seatbelt pretensioners.
One limitation associated with target tracking data available from a radar system is that it is often unable to reliably and/or accurately identify features of the target such as its size, mass, center of mass location, and/or structural information. Such target information may be useful in determining the optimum vehicle response to a possible or impending collision with the target.
It may be difficult for a conventional radar system to obtain highly accurate positional and dynamic information on the target vehicle. The total radar return of a target vehicle is a composite made up of separate and discrete reflections from many different parts of the vehicle, such as the grille, side view mirrors, door panels, etc. These parts are generally at different orientations to the radar antenna at any given time and have differing reflectivities. Accordingly, as the target vehicle moves relative to the radar-equipped vehicle, the total radar cross-section of the target changes and the apparent position of the target""s centroid changes. The resulting variations in the target""s radar return may make it difficult to track the target vehicle with the degree of accuracy required for crash avoidance/mitigation purposes.
It has been proposed to equip vehicles with passive transponders that continually emit radio signals carrying information (in digital or other coded form) describing static and/or dynamic characteristics of the vehicles. Each vehicle is also equipped with a compatible receiver system for receiving and decoding the transponder transmissions from other vehicles. This allows all properly equipped vehicles to xe2x80x9cknowxe2x80x9d pertinent information about the other vehicles in the driving environment.
Driving environments, however, commonly involve dozens of vehicles in relatively close proximity to one another. If all vehicles are equipped with passive transponders, any single vehicle will be receiving the transponder signals from all of the other vehicles in its environment. A vehicle must therefore be able to decode all of the received signals, extract the target information, and match the target information with the correct target vehicle identity and location. The vehicle must therefore process a great deal of information in order to yield results that may be used to take collision avoidance/mitigation actions. Such processing may make the system slower than is desirable in a dynamic driving environment.
The present invention is directed to a method and apparatus for permitting a host automotive vehicle to avoid or mitigate the consequences of a collision between the host vehicle and a target automotive vehicle by using a combination of radar derived target information and transponder information.
The host vehicle is equipped with a radar system operative to scan a sector of the host vehicle""s environment, detect the target vehicle and generate target data such as the range, relative bearing, relative velocity, and relative acceleration of the target vehicle.
The host vehicle is further equipped with a computer which utilizes the radar target data to determine a likelihood of collision between the host vehicle and target vehicle. If the likelihood of collision is, above a certain level, the computer directs the radar system to transmit a directional interrogation system toward the target vehicle. The target vehicle is equipped with one or more transponders that receive the interrogation signal and respond by transmitting a response signal containing information indicating various dynamic and/or static characteristics of the target vehicle. The response signal is received by the host vehicle and is decoded to extract the target vehicle information. The computer then uses the transponder-derived target information along with the radar-derived target information to accurately determine appropriate changes in performance of one or more systems of the host vehicle in order to avoid or mitigate the consequences of the collision.
According to another aspect of the invention, the radar system comprises an electronically scanned antenna capable of transmitting both the scanning radar signal for detecting the target and the directional interrogation signal. The electronically scanned antenna is well adapted to the dual purpose, and is able to generate a relatively narrow beam of RF energy as is desirable for the interrogation signal.
According to another aspect of the invention, the target vehicle is equipped with at least two transponders that transmit distinct response signals. The computer on the host vehicle is able to distinguish between the two response signals and is thereby able to determine an orientation of the target vehicle relative to the host vehicle. This orientation may be determined by comparing one or more characteristics of the two transmitter response signals such as time of arrival, angle of arrival, or phase shift.
According to another aspect of the invention, the information contained in the response signal indicates a relative bearing of the host vehicle with respect to the target vehicle. In an embodiment disclosed herein, this is achieved by transmitting a response signal comprising a reference phase signal radiating in all directions from the target vehicle, and a variable phase signal rotating through 360 degrees. The reference phase signal and the variable phase signal are in phase when the variable phase signal passes a reference bearing of the target vehicle (preferable a bearing of 0 degrees or dead ahead), and at all other bearings the two signals are out of phase by an amount equal to an angle between the bearing of the variable phase signal and the reference bearing. Thus, the host vehicle can determine its bearing relative to the target vehicle by calculating the phase difference between the two signals.
According to still another feature of the invention, the radar system antenna comprises at least two separate antennas mounted at different positions on the host vehicle, whereby differences in the response signal as received at the two antennas allows the computer to determine the orientation of the target vehicle relative to the host vehicle.